Alterations in the differentiated state of the smooth muscle cell (SMC) play a key role in the development and/or progression of a variety of cardiovascular diseases. The goal of this project is to elucidate the role and mechanisms whereby transforming growth factor beta (TGFbeta) signaling pathways control SMC differentiation-maturation during vascular development, as well as during vascular injury in adult animals. The underlying hypothesis is that TGFbeta signaling pathways play a critical role in the initial induction of SMC differentiation marker genes during early vascular development, as well as in sustained expression of these genes in cells already committed to the SMC lineage. Moreover, we hypothesize that the effects of TGFbeta are mediated at least in part through TGFbeta control element (TCE)/TCE binding factor (TCEBF)-dependent pathways identified in our previous studies in cultured cells, and that these processes are also important in controlling alterations in expression of SMC marker genes following vascular injury. We will test these hypotheses by addressing three specific aims. Aim 1 is to define the role of TGFbeta signaling pathways in control of SMC differentiation and maturation in vivo during vascular development, and in in vitro models of early SMC differentiation. Studies will include determining: 1) the spatial-temporal expression patterns of TGFbeta1, and TGFbeta receptors during initial investment of blood vessels with presumptive SMC; 2) if inhibition of TGFbeta1 signaling pathways blocks differentiation of multipotential cells to SMC lineages in vitro; and 3) if SMC specific abrogation of TGFbeta signaling using our unique SMC specific mouse gene targeting system inhibits SMC differentiation-maturation in vivo. Aim 2 is to determine molecular mechanisms whereby TGFbeta1 stimulates expression of SMC differentiation marker genes. Studies will test if effects of TGFbeta1 are mediated through TCEBFs (e.g. BTEB2 and GKLF) identified in our yeast one-hybrid screens, and will include determining: 1) expression patterns of TCEBFs during vasculogenesis; 2) effects of SMC-targeted knockout or over- expression of TCEBFs in vivo; and 3) if effects of TCEBFs involve interactions with TGFbeta SMAD signaling proteins. Aim 3 is to determine the role of TGFbeta signaling mechanisms in control of SMC growth and phenotypic modulation following vascular injury in vivo. Studies will use a novel transgenic mouse injury model developed in our lab, and include determining the effects of SMC targeted knockout of GKLF and TGFbeta receptor signaling pathways. Taken together, studies will provide key insights regarding cellular/molecular mechanisms that control differentiation of SMC, and contribute to understanding the role these processes might play in development of cardiovascular disease.